The present invention relates to an impact protection device for arrangement the steering wheel of a truck vehicle. In a truck vehicle, the steering wheel has a rim that is typically located in a plane inclined at an angle of less than 45xc2x0 to the vehicle longitudinal axis or to a horizontal plane.
Impact protection with an inflatable airbag has been known for arrangement in passenger car steering wheels since many years and have since become standard equipment on modern passenger cars.
Steering wheel air bags are being conceived and offered to an increasing extent also for heavy commercial vehicles, where the steering column is usually arranged substantially more inclined than in the case of passenger cars, resulting in a less inclined orientation of the steering wheel rim. Under these conditions, a conventional airbag system would fail to provide an optimum protection. In fact, in the case of passenger car steering wheels the inflated airbag attains a shape in which the impact surface area is located roughly parallel to rim of the steering wheel. This impact surface area is oriented approximately perpendicular to the impact direction of the upper part of the body of the passenger car driver so that the maximum possible impact surface area and thus best-possible impact protection is achievable in an accident situation.
Such an airbag system, when used in a commercial vehicle steering wheel, would result in an impact surface area of the gas or air bag oriented at a more or less greater angle to the upper part of the body of the driver in impact therewith and which in an accident situation would first come into contact at the bottom before progressively increasing contact upwards. Such an impact response would result, on the one hand, in the impact surface area being initially relatively small and, on the other, the inflated gas bag being displaced in the direction of vehicle travel, thus resulting in the danger of the driver impacting the lower part of the steering wheel, i.e. achieving protection only to an exceedingly deficient degree.
The present invention provides an improved impact protection device for use in the steering wheel rim of a heavy commercial vehicle. According to the invention, the device comprises an inflatable gas bag which, in an inflated condition, assumes the shape of a mushroom with an annular outer edge portion engaging about and behind the steering wheel rim.
The shape of an inflated gas bag depends on the shape of the fabric portions employed and on the arrangement of internal tethers. Accordingly, the shape of the inflated gas bag may be influenced to a major extent, whereby an optimized shape of the inflated gas bag can be easily established by trial and error.
By configuring the gas bag so that it assumes the shape of a mushroom in accordance with the invention when inflated this achieves, for one thing, that the critical lower region of the steering wheel in commercial vehicle steering wheels is covered and, for another, that displacement of the gas bag parallel to the plane of the steering wheel rim is prevented.
In another aspect of the invention, an abutment member activatable together with the gas bag is provided which is instantly movable from a retracted position into an activated position and which in the activated position prevents displacement of the gas bag parallel and relative to the steering wheel rim. Preferably, a pyrotechnic drive is used for instantly moving the abutment member to its activated position.